1. Field of the Invention
The present invention relates to a system and method for measuring round-trip delay and jitter in an optical network.
2. Background of the Prior Art
A Passive Optical Network (PON) is a point-to-multipoint, fiber to the premises network architecture in which unpowered optical splitters are used to enable a single optical fiber to serve multiple premises, typically 32. A PON consists of an Optical Line Termination (OLT) typically at the service provider's central office and a number of Optical Network Units (ONUs) near end users. A PON configuration reduces the amount of fiber and central office equipment required compared with point to point architectures. Downstream signals are broadcast to each premises sharing a fiber. Encryption is used to prevent eavesdropping. Upstream signals are combined using a multiple access protocol, typically time division multiple access (TDMA). The OLTs “range” the ONUs in order to provide time slot assignments for upstream communication and to equalize round trip transmission delays from ONU's on the PON to the OLT
There are a number of standard types of PON that have been implemented. APON (ATM Passive Optical Network) was the first Passive optical network standard. It was used primarily for business applications, and was based on ATM. BPON (Broadband PON) is a standard based on APON. It adds support for WDM, dynamic and higher upstream bandwidth allocation, and survivability. GPON (Gigabit PON) is an evolution of BPON. It supports higher rates, enhanced security, and choice of Layer 2 protocol (ATM, GEM, Ethernet). GPON represents a significant boost in both the total bandwidth and bandwidth efficiency through the use of larger, variable-length packets. A GPON network delivers up to 2,488 megabits per second (Mbit/s) of downstream bandwidth, and 2,488 Mbit/s of upstream bandwidth. GPON Encapsulation Method (GEM) allows very efficient packaging of user traffic, with frame segmentation to allow for higher Quality of Service (QoS) for delay-sensitive traffic such as voice and video communications.
In order to verify the quality of transmitted traffic in a GPON, a number of parameters of the network must be measured and reported to network operations center. Among these parameters are the roundtrip delay of packets in the network and the jitter introduced by the network. Although these important parameters must be measured, it is also important to perform the measurements in a cost-effective manner. Therefore, a need arises for a technique that provides accurate measurement of delay and jitter in a GPON, but which does so in a cost-effective manner (primarily by adding very little, if any cost, at the ONU end)